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JABOD dimensions

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i have been looking around the forum but im finding it hard to find exact details for the dimensions. i want a sideblast.

what is a good size for the fire bowl?

how far from the bottom of the bowl should the tuyere protrude? how much space above the tuyere to the surface?

how big should i make top surface? obviosly bigger will hold more fuel, but what is a practical size?



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Big stock and large projects need a big fire. Small stock and small projects need a smaller fire.

What size stock do you need to get hot?  Just the ends or a workable length, workable meaning how much length can you hammer out before the metal needs reheated?

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I made mine roughly 4" x 8", the size of my fist by the size of two fists. There is an inch under the tuyere and somewhere between 2" and 4" above it. 

I will note that I've noticed it being hard to heat longer stock on my forge. The hot spot was a little low which had me tilting my stock down into the fire. So I had to cut about an inch off of where I put my stock to make it level again. I might have to do the same on the opposite side for longer stock.

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Depends on the fuel and the tuyere size. Charcoal likens tuyeres 3/4-1” ID, that is 1” under the tuyere, and 3-4” over it. This will heat 1” stock easily. I prefer a trench 4x8” 

I easily heated this pick in the forge. 




Below you will find an article that showed side blast forges suitable for charcoal or coal, 1” to the square. At the bottom of the article is a chart for larger tuyeres for coal forges

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Ok, so you found the solid fuel forge section, scroll down the pinned posts at the top  you will find the article in question. 

“Anatomy and brief history of the side blast forge”

45mm inside diameter is a bit large for charcoal, 20-25mm is more appropriate. 

45mm will heat 6” stock with coal and a good air supply.

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aha sorry i didnt realise you were referring to a sticky. i have looked at that before but it seems to conflict with other info in the forum.

for instance you suggest 3/4 over the tyuerre, but the table suggests 5", which is a totally diffrent scale.

i think my fan and tyuerre are a bit oversized, i plan to dump some of the air. will having a reduction nozzle make much diffrence?


cheers Charles


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Yes, I see were that would cause confusion. In the US a commonly available pipe size is 3/4” (.75”) schedule 40 black gas pipe, which acualy has an ID close to 7/8” (schedule 80 is a slip fit 3/4” rod) with charcoal it seems to be happy at 4” and as it is 1/2 way between the 3/4” and 1” ID tuyeres listed on the chart (4” and 5” below hearth hight respectively). 

Charcoal being so light and allowing the fire to spread threw the entire mass of fuel ( charcoal has a very porous nature and reacts differently to coal) really doesn’t do well with large tuyere and fire sizes, if one looks at the twists in historical examples one can clearly see that they were made 6’ at a time in charcoal forges vs the longer twists made later with coal.

Tuyere size with coal is a mater of effecency and stock size, wile I can  heat 1/4” stock in a forge with a 2” tuyere it will eat me out of house and home, but if 6 of my closest friends get to gether to forge a 500# anvil a floor forge with a 2” tuyere would be the beast.

some form of air control is required, Double bellows use weights on the top leaf, box bellows use the spreed you pump (as do paired bellows of the Viking era). Hand blowers depend on speed and driven blowers either use speed ( speed control on electric motors can be iffy as not all types of motors play well with risitors) some form of gate valve/damper or a waste gate ( a simple set up is acualy to provide a gap and point the air flow more or less at the tuyere opening)

Measuring up from the bottom of the JABOD forge is 2” of clay ( brick would be better as you can’t dig threw it cleaning the fire) 1” to the bottom of the tuyere opening ( ash and in the case of coal, or dirty charcoal and burnt steel, slag collect below the air inlet) then from the top of the opening of the tuyere is 4”. 

This is the second build (mark II if you will. Or 2.0 for you kids) my first used a double acting bed pump (nearly worn out) and a 1/2” schedule 40 pipe tuyere. Experimentation brought me to 4” from hearth to top of tuyere. I have bought a new bed pump and as it is one, quieter, two shuts off between heats and three I am less likely to get distracted and burn up my steel, may prefers air source for small charcoal forges (works for soft smithing coal as well, but not for hard coal as it will go out between heats). 

As to reducing your tuyere, I would think sourcing a pipe cap that will fit and drilling a hole in it. Will work as will a pipe reducer if you can’t just replace the tuyere. Heck you may be able to push a new tuyere threw the old one. 

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i really appreciate your input. im english and i was taught in metric at school, so i apologise for getting a bit confused. the way imperial measurments are written and vocalised, i have to consciously think about convert back to something i can undertsand.


i would be tempted to use coal but its not really available here. in my area we have ancient coppice woodland and really good quality charcoal.


im currently making an air gate. im not sure if i can find an end cap as cast iron has been out of use for decades, so im not sure how i can reduce the tuyere down. 

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A simple plate with a hole will work just fine.

i was taught both in school, so tho imperial is my first choice do to living stateside, I am equally versant. Tho conversion dose slow me down. 

Charcoal is a very nice fuel to use in small forges, as it is very clean.

personaly I am waiting for Jerry to flat-rate me a chunk of soap stone (3500f natural refractory) for a bellows stone/tuyere

sorry for the disjointed nature of my reply, multi tasking.

as to the 3/4” and the 3 to 4” confusion that on me, America mixes and matches communication formats and what is clear to my mind is certainly not guaranteed to be clear to you. In American English you learn to read for context 

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The comma usage in the place of our decimal point is encountered in much of Europe. But you can, also, find it in Quebec.

JHCC it is 'commic', but not always. I remember reading a reported law case involving a contract between a French company and an American one. The American company was not aware of the different usage. That misapprehension cost them tens of thousands of dollars. They sued in order to have the contract annulled. But the French court was not buying it and they lost.

The moral of the story is hire a local consultant or law firm to go over the contract.

Please don't ask me for the reference. It was years ago and I do not even remember where I read it.



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